Journal of the Korean Recycled Construction Resources Institute (한국건설순환자원학회논문집)

Korean Recycled Construction Resources Institute (한국건설순환자원학회)
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Evaluation of Chloride Diffusion Characteristics in Concrete with Fly Ash Cured for 2 Years

2년 양생된 Fly Ash 콘크리트의 염화물 확산 특성 평가

  • Yoon, Yong-Sik (Department of Civil and Environmental Engineering, Hannam University) ;
  • Hwang, Sang-Hyeon (Department of Civil and Environmental Engineering, Hannam University) ;
  • Kwon, Seung-Jun (Department of Civil and Environmental Engineering, Hannam University)
  • 윤용식 (한남대학교 토목환경공학과) ;
  • 황상현 (한남대학교 토목환경공학과) ;
  • 권성준 (한남대학교 토목환경공학과)
  • Received : 2018.11.27
  • Accepted : 2019.02.21
  • Published : 2019.03.30
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Abstract

When RC(Reinforced Concrete) structures are exposed to harsh environment, deterioration phenomenon occurs, and the corrosion in rebar due to chloride intrusion is known as representative deterioration, so called chloride attack. In this paper, chloride resistance performance of 2 years aged concrete is evaluated considering 3 levels of water to binder ratio(0.37, 0.42, and 0.47) and 2 levels of substitution ratio of fly ash(0% and 30%). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests referred to KS F 2405 are performed. With adaptation of the previous test results and the results from this study, time-dependent chloride diffusion characteristics are analyzed for each concrete. The FA(Fly Ash) concrete has higher chloride resistance performance than OPC(Ordinary Portland Cement) concrete. According to the evaluation standard of ASTM C 1202, the FA concrete has "Moderate" grade after 49 days while OPC concrete does "Moderate" grade after 365 days. As the results of time-parameter for chloride diffusion, OPC concrete and FA concrete show the decreasing behavior of time-parameters with increasing water to binder ratio. Also, FA concrete has 1.57~2.74 times of time-parameter than OPC concrete. That's cause is thought that the time-parameter indicates the gradient of decreasing of diffusion coefficient. FA concrete has higher time-parameters than OPC concrete by pozzolanic reaction of FA.

콘크리트 구조물이 극심한 열화 환경에 노출되는 경우 열화현상이 발생하게 되는데, 대표적인 열화 현상으로는 염해에 의한 철근부식이 있다. 본 연구에서는 3가지 수준의 물-결합재 비(0.37, 0.42, 0.47) 및 2가지 수준의 플라이애시 치환율(0%, 30%)을 고려하여 재령 2년 콘크리트 시편을 대상으로 염해 저항 성능을 평가하였다. Tang's method에 준하여 촉진 염화물 확산계수를, ASTM C 1202에 준하여 통과 전하량을, KS F 2405에 준하여 압축강도를 평가하였다. 또한 기존의 제안식들과 촉진 염화물 확산계수 결과를 활용하여 각 배합의 시간의존성 확산 특성을 분석하였다. 플라이애시 혼입 배합은 OPC 배합 대비 뛰어난 내구성능을 나타내는데, 통과 전하량 평가기준에 따르면 재령 49일부터 "Moderate" 등급 이하에 포함되는 반면 OPC 배합은 재령 1년에서야 모든 물-결합재 비에서 "Moderate" 등급 이하에 포함되었다. 각 배합의 시간의존성지수를 도출한 결과 모든 배합에서 물-결합 재비가 증가함에 따라 시간의존성지수가 감소하는 경향을 나타내었다. 또한, 플라이애시 혼입 배합에서 OPC 배합 대비 1.57배~2.74배의 시간의존성지수가 평가되었다. 이는 시간의존성지수가 확산계수가 감소하는 기울기를 나타내기 때문이며, 플라이애시의 포졸란 반응에 의해 FA 배합에서 OPC 배합 대비 높은 시간의존성지수를 나타내었다.

Keywords

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Fig. 1. Mimetic diagram and test condition for Tang’s method

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Fig. 2. Test results for diffusion coefficient considering W/B and substitution ratio of FA

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Fig. 3. Decreasing ratio in accelerated diffusion coefficient by curing effect

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Fig. 4. Test results for passed charge considering W/B and substitution ratio of FA

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Fig. 5. Decreasing ratio in passed charge by curing effect

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Fig. 6. Test results for compressive strength considering W/B and substitution ratio of FA

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Fig. 7. Increasing ratio in compressive strength by curing effect

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Fig. 8. Results for time-parameter by regression analysis

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Fig. 9. Comparative evaluation of time-parameter

Table 1. Concrete mixture for this study

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Table 2. Properties of sand and gravel

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Table 3. Properties of super plasticizer

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Table 4. Evaluation standard for chloride resistance by ASTM C 1202

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